Cap 1 Termodinâmica q

8/12/2019 Cap 1 Termodinmica q

1/21

Captulo 1

Termodinmica Qumica

Professor Osvaldo Chiavone Filho

DEQ/UFRN

2013.2


2/21

THE SCOPE OF

THERMODYNAMICS

The science of thermodynamics was born in the nineteenth

century of the need to describe the operation of steam engines

and to set forth the limits of what they can accomplish. Thus the

name itself denotes power developed from heat, with obviousapplication to heat engines, of which the steam engine was the

initial example. However, the principlesobserved to be valid for

engines are readily generalized, and are known as the first and

second laws of thermodynamics. These laws have no proof in themathematical sense; their validity lies in the absence of contrary

experience. Thus thermodynamics shares with mechanics and

electromagnetism a basis in primitive laws.


3/21

THE SCOPE OF

THERMODYNAMICS

These laws lead through mathematical deduction to a network of

equationswhich find application in all branches of science and

engineering. The chemical engineer copes with a particularlywide

variety of problems. Among them are calculation of heat and workrequirements for physical and chemical processes, and the

determination of equilibrium conditions for chemical reactions and

for the transfer of chemical species between phases.

Thermodynamic considerations do not establish the rates of chemicalor physical processes. Rates depend on driving force and resistance.

Although driving forces are thermodynamic variables, resistances are

not. Neither can thermodynamics, a macroscopic-property

formulation, reveal the microscopic (molecular) mechanisms of

physical or chemical processes.


4/21

THE SCOPE OF THERMODYNAMICSOn the other hand, knowledge of the microscopic behavior of matter

can be useful in the calculation of thermodynamic properties.Property values are essential to the practical application of

thermodynamics. The chemical engineer deals with many chemical

species, and experimental data are often lacking. This has led to

development of "generalized correlations that provide propertyestimates in the absence of data.


5/21

TYPES OF THERMODYNAMICS


6/21

The application of thermodynamics to any real problem starts with

the identification of a particular body of matter as the focus ofattention. This body of matter is called the system, and its

thermodynamic state is defined by a few measurable macroscopic

properties. These depend on the fundamental dimensions of science,

of which length, time, mass, temperature, and amount of substanceare of interest here.

APPLICATION OF THERMODYNAMICS

P = presso

T = temperatura

x= composio

= densidade


7/21

Projeto de Processos

(Ex. Extrao por Solvente)

1

2

3

4

5

67

8

9

10

11

12

13

14

15

W1

11

T1

W2

T2

12

32

W3T

3

13

23

W7

T7

W6

T6

W4

T4

Vd

Ae

W5

T5W

8T8

W9

T9

W10

T10

W11

T11

W12

T12

Ac

Ar

W13

T13

W14

T14

W15

T15

14

24

extrato

rafinado produto

guagua

vapor

EVAPORADOREXTRATOR

CONDENSADORRESFRIADOR

MISTURADOR

alimentao

bomba

decantador

solvente

condensado

f

f

f

f f

f

f

f

x11

x14

31

Dimensionamento

Simulao

Otimizao ($)

Anlise de Sensibilidade

W = vazo

T = temperaturaV = volume

A = rea

x= composio

fij= fluxo comp. i

e corrente j


8/21

Avano do Equilbrio Lquido-

Vapor por Conta da Destilao

0.00 0.20 0.40 0.60 0.80 1.00

Frao molar de pentano

300.0

350.0

400.0

450.0

500.0

Temper

atura(K)

Lquido

Vapor

L + V

Experimental

Acima pto Crtico

UNIQUAC

Destilao - Gs de Cozinha T-xy C5+C12 a 100 kPa

Planta Qumica Tpica (50% do $)


9/21

DIMENSIONS AND UNITS

The fundamental dimensions are primitives, recognized through

our sensory perceptions and not definable in terms of anything

simpler. Their use, however, requires the definition of arbitrary

scales of measure, divided into specific units of size. Primary unitshave been set by international agreement, and are codified as the

International System of Units (abbreviated SI, for Systme

International).

Time: s (Cesium cycle)

Length: m

Mass: kg

Mole: symbol mol, is defined as the amount of substance

represented by molecules.


10/21

PREFIXES FOR SI UNITS


11/21

TEMPERATURE, K

Termmetro a Gs Ideal

P v = R T


12/21

Force, N

Exerccio:Um astronauta pesa 730 N em Houston, Texas, onde a aceleraoda gravidade g= 9,792 m s-2. Quais so a massa e o seu peso nalua, onde g= 1,67 m s-2?


13/21

Pressure, Pa

Manmetro a contrapeso

A

mg

A

FP

Ahm

ghA

gAhP


14/21

Pressure, PaQual a presso Pdo tanque com ar indicado pela figura a seguir em

Pa, sabendo que a presso atmosfrica igual 750 mmHg e que omanmetro de mercrio registra uma quota de 35 cm.

760 mmHg = 101325 Pa


15/21

Work, Pa

Diagrama P-V

dlFdW

A

VdAPdW

dVPdW

2

1

V

VdVPW


16/21


17/21

Kinetic EnergyWhen a body of mass m, acted upon by a force F, is displaced a

distance dl during a differential interval of time dt, the work done is

given by F dl.In combination with Newton's second law:

dlamdW dldt

dumdW duumdW

22

2

1

2

22

1

mumuduumdW

u

u

2

2

1muEK

Potential EnergyIf a body of mass mis raised from an initial elevation z1to a final

elevation z1, an upward force at least equal to the weight of the bodymust be exerted on it, and this force must move through the distance

z2-z1. Since the weight of the body is the force of gravity on it, the

minimum force required is given by Newton's law:

gmamF

)()( 1212 zzgmzzFW gzmEP


18/21

Energy ConservationIn any examination of physical processes, an attempt is made to find

or to define quantities which remain constant regardless of the

changes which occur. One such quantity, early recognized in thedevelopment of mechanics, is mass. The great utility of the law of

conservation of mass suggests that further conservation principles

could be of comparable value. Thus the development of the concept

of energy logically led to the principle of its conservation inmechanical processes. If a body is given energy when it is elevated,

then the body conserves or retains this energy until it performs the

work of which it is capable. An elevated body, allowed to fall freely,

gains in kinetic energy what it loses in potential energy so that its

capacity for doing work remains unchanged. For a freely falling body

this means that:

0 PK EE 0

22

12

2

1

2

2 gmzgmzmumu


19/21

HeatWe know from experience that a hot object brought in contact with a

cold object becomes cooler, whereas the cold object becomes

warmer. A reasonable view is that something is transferred from thehot object to the cold one, and we call that something heat Q. Thus

we say that heat always flows from a higher temperature to a lower

one. This leads to the concept of temperature as the driving force for

the transfer of energy as heat. More precisely, the rate of heattransfer from one body to another is proportional to the temperature

difference between the two bodies; when there is no temperature

difference, there is no net transfer of heat. In the thermodynamic

sense, heat is never regarded as being stored within a body. Like

work, it exists only as energy in transit from one body to another, or

between a system and its surroundings. When energy in the form of

heat is added to a body, it is stored not as heat but as kinetic and

potential energy of the atoms and molecules making up the body.


20/21

HeatIn spite of the transient nature of heat, it is often viewed in relation to

its effect on the body from which it is transferred. As a matter of fact,

until about 1930, the definitions of units of heat were based on thetemperature changes of a unit mass of water. Thus the British thermal

unit (commonly known as thermochemical Btu) was long defined as

1/180thquantity of heat which when transferred to one pound mass

of water raised its temperature from ice-point or 32 (F) to steam-point or 212 (F) at standard atmospheric pressure.. Likewise the

calorie (commonly known as thermochemical calorie) written as (cal)

in the book, was defined as 1/100thquantity of heat which when

transferred to one kilogram mass of water raised its temperature

from 0 to 100C (273.15 to 373.15 K) at standard atmospheric

pressure. Although these definitions provide a "feel" for the size of

heat units, they depend on experiments made with water and are

thus subject to change as measurements become more accurate.


21/21

HeatIn order to recognize a common basis for all energy units,

international steam table calorie is defined in relation to joule, the SI

unit of energy, equal to 1 N m. Joule is the mechanical work donewhen a force of one newton acts through a distance of one meter. By

definition, international steam table calorie is equivalent to 4.1868 J

(exact) and thermochemical calorie is equivalent to 4.184 J (exact). By

arithmetic, using the defined relations of US Customary and SI units,one international steam table Btu, written as (Btu) in the book, is

equivalent to 1055.056 J as against one thermochemical Btu is

equivalent to 1054.35 J. All other energy units are defined as

multiples of the joule. The foot-pound force, for example, is

equivalent to 1.355 8 179 J while the meter-kilogram force is

equivalent to 9.806 65 J. The SI unit of power is the watt, symbol W,

defined as energy rate of one joule per second.

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